A drift-kinetic treatment of the parametric decay of large-amplitude Alfven waves

Details A drift-kinetic treatment of the parametric decay of large-amplitude Alfven waves A drift-kinetic treatment of the parametric decay of large-amplitude Alfven waves

Jul 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990jgr....9510525i&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 95, July 1, 1990, p. 10525-10539.

Physics

63

Kinetic Equations, Magnetohydrodynamic Stability, Magnetohydrodynamic Waves, Plasma Decay, Solar Wind, Vlasov Equations, Drift Rate, Ion Distribution, Kinetic Theory, Plasma Drift

Scientific paper

A kinetic formulation for the parametric decay instability of a large-amplitude, circularly polarized Alfven wave based on a drift-kinetic description of the plasma is derived. The formulation is not restricted to a Maxwellian ion plasma but can be used for arbitrarily-shaped ion distribution functions, e.g., those measured in the solar wind. The MHD equations of the instability are recovered for the case that the ions are cold and the electrons carry all the thermal plasma energy. Even a small amount of ion thermal energy reduces the maximum growth rates of the instability below those obtained in an MHD treatment and broadens the unstable wave number range. Conversely, the presence of an ion beam or a plateau in the ion distribution function at velocities below the Alfven velocity may give rise to enhanced growth rates. In the solar wind, the efficiency of the parametric decay instability is reduced both by kinetic effects and by the short correlation time of the driving Alfven waves so that the instability probably cannot compete with the nonlinear energy cascade in shaping the turbulent energy spectra over short distances. However, the parametric decay instability may have an important influence on the reduction of the cross-helicity in the solar wind observed over large scales of the order of 1 AU.

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